Within the technology of casting of metals it is known to apply magnetic fields to the molten metal during manufacturing; this is known as electromagnetic stirring. U.S. Pat. No. 4,523,628 and U.S. Pat. No. 6,443,219 disclose manufacturing methods in which electromagnetic coils are arranged so that they surround the mould at areas where the generated magnetic fields can influence the metal during solidification by generating vibrations in the metal that can result in an improved homogeneous structure.
Application of vibrations during manufacturing in order to improve the microstructure are also known in relation to Metal-Matrix-Nano-Composites (MMNCs) which are alloys with greatly enhanced properties produced by the addition of nano-particles. They typically have around 50% higher strength than similar alloys without reinforcement. One of the problems in manufacturing these alloys concerns the difficulty in distributing the nano-particles evenly in the alloy matrix, especially where large components are to be manufactured. Today cast MMNCs are mixed and made using ultrasonic acoustic probes (sonotrodes) operating at frequencies around 20 kHz. The sonotrodes are immersed in the liquid material to encourage wetting of the NPs, the breaking up of agglomerations by cavitation and their distribution via sound-induced convection. Ultrasound treatment is also used during casting of unreinforced metals, such as for degassing and in order to refine the microstructure. The sonotrodes need to be replaced frequently as they erode in reactive metals and at the same time contaminate the melt. This may particularly be the case for materials having a high melting point, such as Ti, Fe, Mo and Zr. Furthermore, where a large volume is to be treated, multiple sonotrodes may be used, introducing complexity and increased cost.